The present invention relates to a vibration energy harvester for converting mechanical vibrational energy into electrical energy. The present invention also relates to a method of operating a vibration energy harvester for converting mechanical vibrational energy into electrical energy, including during an installation phase. In particular, the present invention relates to such a device which is a miniature generator capable of converting ambient vibration energy into electrical energy for use, for example, in powering intelligent sensor systems. Such a system can be used in many areas where there is an economical or operational advantage in the elimination of power cables or batteries.